1. Field of the Invention
The present invention relates to a hand device of a working robot for gripping a workpiece, and particularly, the hand device which includes a workpiece drop prevention means which operates in an emergency or the like, such as an electric power failure.
2. Description of Related Art
Conventionally, a hand device for working robot is known which comprises a workpiece drop prevention means for preventing a workpiece from dropping by maintaining a gripping state so as not to drop or displace the workpiece even if an electric power failure and a malfunction or a disorder of a driving system occurs while the workpiece is delivered or reversed. As one of such apparatus, for example, Japanese Patent publication of unexamined application No. 06-114778 discloses a workpiece drop prevention means of a robot hand comprising a chuck arm for gripping a workpiece from both lateral sides using the linear movement along a guide member, a chuck cylinder for driving the gripping movement of the chuck arm, a rail for lock having one end connected to the guide member and the other end connected to an eccentric cam, and a lock cylinder for locking the rail for lock by a rotation of the eccentric cam for lock in order to prevent the rail for lock from moving to the outside.
Under the condition that the hand is gripping a workpiece, the major axis of the eccentric cam rotates in the direction of the rail for lock by means of the lock cylinder, so that the periphery of the major axis attaches to the rail for lock to engage with the same. Thus, in this robot hand, even in an emergency where the gripping force of the chuck arm is decreased by a chuck cylinder, a movement of the chuck cylinder to open outward makes the rotating diameter of the eccentric cam larger. Whereby, a locking state is strengthened to stop the chuck cylinder, so that a workpiece can be prevented from dropping.
However, in a robot hand in the above, as the periphery of the major axis and the rail for lock are engaged every time a workpiece is gripped, a dent or a scar easily occurs at a portion where the periphery and the rail attach each other. As a result, the length of the major axis of the eccentric cam which is a diameter of rotation comes inconsistent. This causes a change of a rotating torque that is pressing force applied to the attaching portions. Under such circumstances, a controlling means for fine adjustment of an elasticity of the lock cylinder is needed in order to keep the pressing force of the eccentric cam applied to the rail for lock within a desirable value. Thus, a configuration of the workpiece drop prevention means becomes complicated.
Further, with this robot hand, a workpiece is gripped by a linear movement of a chuck arm along the guide member. Thus, the length of the guide member should be secured to be longer than the width of grip portion of the workpiece, which makes it impossible to downsize the guide member less than the width of the grip portion of the workpiece. Moreover, since an eccentric cam and a rail for lock are engaged by friction, the chuck arm could not always be stopped due to a stain on an attaching portion or abrasion during the elapsed time. Therefore, there is a problem that the reliability of a workpiece drop-prevention function could be lowered.
Considering the above problems, the object of the present invention is to provide a hand device for working robot which can be downsized including a workpiece drop prevention means with a simple configuration and further enabling to improve reliability of a workpiece drop preventing function.